Electrical connection



June 12, 1962 R. c. SWENGEL 3,038,958

ELECTRICAL CONNECTION Filed June 8, 1959 5 Sheets-Sheet 1 & I I \\'l 28 25 INVENTOR- 30 Robert. C. Swenye/ 25 186 a BY June 12, 1962 R. c. SWENGEL 3,038,958

. ELECTRICAL CONNECTION Filed June 8, 1959 3 Sheets-Sheet 2 I6 20 \V 20 5e IN V EN TOR.

Robert C. Swenqe/ BY Ha a June 12, 1962 R. CNSNNENGEL 3,038,958

ELECTRICAL CONNECTION Filed June 8, 1959 3 Sheets-Sheet 3 INVENTOR. Robe H. C. Swe BY United States 3,038,953 ELECTRICAL CONNECTION Robert C. Swengel, Hellam, Pa., assignor to AMP Incorporated, Harrisburg, Pa. Filed June 8, 1959, Ser. No. 818,845 4 Claims. (Cl. 174-34) This invention relates to swaged electrical connections. The term swaged, as employed herein, is intended to refer to connections formed by pressing or hammering the wire and terminal,

An object of the invention is to provide a swaged connection having improved mechanical and electrical characteristics. A further obiect is to provide a connection which can be formed with relative ease and requires only a relatively simple terminal. A further object is to provide a swaged connection in which the elastic recovery of the terminal after the swaging operation is utilized to maintain the contact between the terminal and the wire. A further object is to provide a swaged connection in which the wire is drastically deformed during swaging to produce fresh metal surfaces for the wire-connector interface.

These and other objects are attained in a terminal having an elongated groove into which the wire is pressed for a substantial portion of its length. In one preferred embodiment, the groove is of a width less than the wire diameter so that, during swaging, the edges of the groove scrape and clean the wire to expose fresh metal surfaces for the wire-terminal interface. The terminal is loaded or stressed by the wire during swaging and the sidewalls of the groove are sprung apart. Thus, these sidewalls tend to spring together after the swage has been made and grip the Wire by virtue of this fee.

In the drawings:

FIGURE 1 is a perspective view of one form of terminal adapted to be swaged to the wire in accordance with the invention;

FIGURE 2 is a perspective view of the terminal of FIGURE 1 have a wire swaged thereto and secured to a printed circuit board;

FIGURES 3 and 4 are cross-sectional views illustrating the method of forming swaged connections;

FIGURE 5 is a cross-sectional view of a finished swaged connection in accordance with the invention taken along the lines 55 of FIGURE 1;

FIGURES 6 and 7 show the swaging of an alternative form of the invention;

FIGURES 8 and 9 show the swaging of another alternative embodiment;

FIGURES 10 and 11 show the manner in which the wire is cleaned or stripped of varnish-type insulation in the practice of the invention;

FIGURES 12 and 13 show alternative forms of the invention in which the terminal is swaged to a plurality of wires;

FIGURE 14 is a cross-sectional view illustrating the manner of forming electrical connections when using the terminal of FIGURE 13; and

FIGURES l5 and 16 show an embodiment in which a terminal having a relatively wide groove is used,

Referring now to FIGURES 1-5, a terminal 2 adapted to be swaged onto a wire in accordance with the invention comprises a relatively elongated metal slug having arms 4 prO ecting therefrom adjacent one end. Terminals of this type, which are commonly known to the art, are inserted through a printed circuit board 6 having metallic circuit means 8 on at least one side, and are upset or split as shown at id to secure them to the board. The board is solder dipped to deposit a solder mass 12 which 3,038,958 Patented June 12, 1962 ice establishes an electrical connection between the terminal and the circuit means.

The terminal provides a relatively elongated groove 14 having sidewalls l6. The sidewalls advantageously extend divergently from the surface as shown in FIGURE 3, and the groove is adapted to receive a wire 18 in the manner shown in FIGURES 3-5. The wire is first positioned axially over the groove and against the edges 20, while the underside of the terminal is supported on a suitable tool anvil 22. In the embodiment of FIGURE 3, anvil 22 is of about the same width as the width of the terminal, and the underside 25 of the terminal is flat as shown. For reasons which are explained below, a substantial section of the length of the wire should be positioned over the groove, and the supporting anvil 22 should extend for the same substantial distance along the underside of the terminal and beneath the wire. By the term substantial length, it is intended to imply that the length of wire positioned over the groove is about three or more wire diameters. The benefits of the invention are not achieved to the fullest possible extent if the length of wire pressed into the groove is equal to or less than the diameter of the wire.

The pressing of the wire into the groove is achieved by means of a suitable tool member or die 26, which engages only the wire and not the terminal, so that all of the force applied is transmitted through the wire. As the force is applied and its magnitude increased, the edges 20* of the groove bite into the wire and the wire itself flows laterally beyond these edges, as shown at 28, and downwardly into the groove as shown at 30. Thus, during the pressing operation, the forces transmitted through the wire are applied to the edges 20 of the groove, as indicated by the arrows of FIGURE 3. These edges are, as a result, sprung apart to some extent, although the amount by which they are sprung apart is very slight. The wire is pressed further into the groove and advantageously, until it entirely fills the cross section thereof, as shown in FIG- URE 5, and the portion of the wire which is extruded laterally, forms a crown 32. After pressing, the wire has a T-shaped cross section with the crown of the T extending beyond the edges of the groove. In the embodiment of FIGURE 5 and in the other embodiments shown, the cross-sectional area of crown 32 is approximately equal to the cross-sectional area of the groove. In other words, after swaging, about one half of the cross section of wire is in the crown and the other half is in the groove. This ratio is not critical, however, and the crown may be relatively larger or smaller than the embodiment of FIGURE 5 depending on the wire size; i.e. if a larger diameter wire is employed, a larger crown will result, and if a smaller wire is employed, a smaller crown will result.

In the finished connection of FIGURE 5, the portion of the wire contained between the sidewalls 16 is in compression and is pinched between the sprung-apart sidewalls. The stress pattern of the terminal, as viewed in transverse cross section, is similar to the stress pattern of a C-clamp having an object clamped and compressed between its jaws. In other words, a neutral (unstressed) axis N extends from each sidewall outwardly and downw'ardly, and beneath the groove. The metal within this axis and adjacent the groove is in tension while the metal beyond this neutral axis is in compression. Of course, the exact location of this neutral axis is not readily determinable and will undoubtedly be dependent upon the exact geometry of the parts and the physical properties of the material involved. However, in general, the C-clamp analogy explains the holding action of the terminal on the wire. The amount of flexure which is imparted to the terminal may not be discernible to the unaided eye; however, such flexure is present in the terminal by virtue of the manner in which it is loaded by the wire.

A variety of some of the possible alternative embodiments of the invention is described below; however, the fundamental advantages of the invention which are common to all embodiments can be appreciated from a consideration of FIGURE 5. An important advantage is that the tendency on the part of the terminal to return to its original shape, or to relieve itself of the stresses imposed upon it during crimping, contributes to and enhances the electrical and mechanical properties of the connection. Referring to FIGURE 5, and assuming that the bending stresses in the terminal are all lower than the elastic limit of the metal of the terminal, it is apparent that if the wire were removed from the groove, the terminal would assume its original cross-section-al geometery and the sidewalls of the groove would move relatively towards each other. Thus, while the wire is in the terminal, these sidewalls are continually urged against the portion of the wire which is contained within the groove. If the wire should undergo metallic creep (i.e. slowly lengthen and reduce its crosssectional area) during the life of the connection, the sidewalls would follow the wire by moving relatively towards each other and the interfacial contact between the wire and the terminal would be maintained. Thus, connections in accordance with the invention are provided with a built-in take-up device to maintain the integrity of the connection in the event of dimensional changes in the Wire resulting from creep or temperature effects.

This advantage is achieved, in part at least, as a result of the fact that the load applied to the terminal during crimping is applied through the wire so that, in effect, the wire functions as a means of stressing the terminal. It will be recalled that with many prior art terminals, crimping is accomplished by applying the crimping force directly to the terminal and transmitting the forc through the terminal to the wire. For example, terminals of the type having a tubular ferrule are usually crimped by indentation or by flattening between the jaws of a crimping tool. It is necessary with such ferrules permanently to deform the terminal (i.e. stress it beyond its yield point) in order to crimp it onto the wire. It is known, however, that metals which have been permanently (i.e. plastically) deformed in this manner retain some elasticity, and that they exhibit some dimensional recovery (i.e. spring bac after the external load has been removed. Thus if a tubular ferrule is flattened into gripping engagement with a wire between the jaws of a crimping tool, the terminal will open up slightly after the tool is removed, and such relaxation reduces the contact pressure and detracts from the integrity of the connection. With the instant invention, on the other hand, relaxation by the terminal after removal of the crimping tool contributes to the quality of the connection.

It is not intended to imply by the foregoing discussion that, in the practice of the instant invention, the terminal cannot be stressed beyond its elastic limit. If the terminal is stressed beyond its elastic limit, the spring back of the metal will cause it to grip the wire in the same manner as the wire is gripped in the case of purely elastic deformation. In other words, regardless of the amount of flexure imparted to the terminal by the wire, the terminal will tend to return at least partially to its original shape and the wire will be gripped as previously described.

Connections in accordance with the invention have good resistance to the eifects of corrosive atmospheres and good mechanical strength. Tests have demonstrated that with properly made connections in accordance with the invention, mechanical failure in a tensile test will occur in the wire at a point remote from the swage and excellent conductance at the swaged connection is obtained. By comparison with many prior art crimped connections, the mechanical strength obtained, Where the crimp is designed for optimum electrical properties, is less than the tensile strength of the wire, but if the crimp is designed for maximum strength, the electrical properties are less than optimum.

A further advantage of the invention is illustrated in FIGURES l0 and 11, wherein the wire has a thin varnishtype insulating coating 4-0 of the type commonly used for coil wires and the like. It has been found from examination of the cross sections of connections that this coating is substantially removed during swaging by the edges 20, and that metal-to-metal contact is obtained along the sidewalls 16 of the groove although the varnish coating will remain on the portions of the wire which are against the bottom of the groove and on the crown as shown at 42 and 44. If the wire is not coated with an insulating varnish, the fact that new clean wire surface is exposed during swaging undoubtedly contributes to the electrical properties of the crimp, in that oxide on other nonconductive coatings on the wire are removed.

For best results, swaged connections in accordance with the invention should satisfy certain conditions with regard to the materials used and the geometry of the terrninal. The wire should be at least as soft and ductile as, and preferably softer than, the terminal. For best practice, the wire is drastically and permanently deformed during swaging while the terminal is elastically deformed or alternatively permanently deformed to only a slight degree. Good results are obtained if the wire is of soft copper and the terminal is of brass or steel. The soft copper wire will readily follow the flow pattern of FIG- URES 3 and 4 during swaging, while the brass terminal will flex elastically to receive the deformed wire.

As previously mentioned, it is desirable that the length of the copper wire which is received within the groove be substantial as compared to the Wire diameter, e.g. it should be about three or more wire diameters. The requirement for a relatively long section of swaged wire is to assure compressive loading of the wire in its transverse plane (FIGURE 5) so that the wire in turn will load the terminal by springing the sidewalls of the groove apart. If the length of wire swaged is relatively short, the wire will tend to extrude axially during swaging and the terminal will not be loaded or sprung apart to the optimum extent. In other words, the interfacial unit pressure (in pounds per square inch) between the wire and the terminal will be lower with a short swage and, of course, the total interfacial area will also be low.

The cross-sectional geometry of the terminal may take a variety of forms provided the groove is spread apart during swagin as previously explained. If the terminal is flat as in FIGURE 1, the anvil can support the terminal under its complete width since the amount of fiexture is relatively slight. It will also be found practical to utilize an anvil as shown in FIGURE 6 at 34, which has a supporting surface wider than the terminal and has upstanding sidewalls 36. An anvil of this type, when incorporated in a swaging tool, has the advantage of locating the terminal relative to the wire and the swaging die. As an alternative to a flat anvil and flat terminal, the upper side of the terminal may be slightly convex as shown in FIGURE 8, but with this type of terminal the die must be arcu-ate in cross section. The terminal is free to flex somewhat as shown in FIGURE 9, and the wire will he gripped by the terminal by virtue of its stressed condition. The type of terminal shown in FIG- URE 8 cannot be used with an anvil having a flat surface, however, since the terminal would be supported only along its lateral edges and, during swaging, the groove would be closed rather than opened.

FIGURE 12 shows an embodiment of the invention having a pair of grooves on opposite sides of the terminal. With this embodiment the terminal is not flexed; however, the grooves are opened during crimping and tend to close onto the wire by virtue of the fact that the stress patterns established by the wires are as previously described. The embodiment of FIGURE 12 provides diagonal parallel grooves for the accommodation of multiple wires on one terminal. Again, the grooves are sprung apart when the wire is swaged and tend to close onto the wire upon removal of the crimping tool.

FIGURES 13 and 14- show an embodiment in which the tab has a reversely bent end section 46 and the grooves extend transversely of the longitudinal axis of the tab in the bent portion. Ordinarily, it is not recommended that the grooves in the tab should extend normally of the longitudinal axis Since, if the tab were flexed, these grooves would be opened up and their grip on the wire would be relaxed. Where the grooves are in the bent portion 46 of the tab, however, such flexure does not give rise to bending stresses in the vicinity of the grooves and the grip on the wire is not relaxed. In swaging the embodiment of FTGURE 13, the bent section of the tab is merely pressed against the unbent pontion by the use of a pair of jaws 48 as shown in FIGURE 14.

FIGURES 15 and 16 show an embodiment in which the groove is relatively wider than the diameter of the wire. The terminal is again stressed as the wire is deformed and the wire is pinched between the sprung-apart sidewalls. This embodiment avoids the scraping action of the wire over the edges of the groove and may be of particular utility where the wire is relatively hard and resistant to plastic deformation.

The foregoing paragraphs describe only some of the many possible embodiments of the invention. It will be apparent that a principal feature of the invention is that the wire itself is relatively drastically deformed and directly transmits the swaging force applied. As a result, the terminal is loaded or stressed by the wire in a manner such that its tendency to revent to an unstressed condition acts to pinch the wire at the wireterminal interface.

I claim:

1. An electrical connection between a terminal and a solid wire comprising, a groove in said terminal, the width of said groove being less than the diameter of said wire and the cross-sectional area of said groove being less than the cross-sectional area of said wire, the sidewalls of said groove being divergent towards the bottom of said groove, a portion of the length of said wire being deformed and pressed into said groove and entirely occupying the cross-section thereof, and the excess metal of said portion being at least partially flattened and extending beyond the edges of said groove, said groove being sprung apart and the sidewalls of said groove exerting a residual pressure on said wire, said groove and wire being in dovetailed relationship to each other.

2. An electrical connection between a terminal and a wire, said terminal comprising a plate-like member having a groove therein, the edges of said groove being relatively sharp and the width of said groove being substantially less than the diameter of said wire, the depth of said groove being such that the cross sectional area thereof is substantially less than the cross sectional area of said wire, said wire having a substantial portion of its length pressed into said groove and deformed to a generally T-shaped cross section with the crown portion thereof extending beyond the edges of said groove, the portions of said groove in which said wire is received being spread apart by said wire and exerting pressure against said wire.

3. A connection as set forth in claim 2 wherein the sidewalls of said groove as viewed in transverse cross section diverge towards the bottom of said groove whereby, said wire and said groove are in dovetailed relationship to each other.

4. A connection as set forth in claim 2 wherein said wire is provided with a varnish type insulation, portions of said insulation having been removed by said groove when said wire was pressed into said groove thereby to establish electrical contact between said wire and said terminal.

Wilkins Jan. 25, 1938 Weder July 18, 1944 

